Motor vehicles are as a rule equipped with tank ventilation systems for setting desired pressure ratios within a fuel tank provided in each motor vehicle. Above all, such systems prevent enrichment of hydrocarbons, which are released from the corresponding fuel, in the gas phase.
So that hydrocarbons do not pass into the environment, the tank ventilation systems for absorbing fuel vapors are provided with special filters, generally activated carbon filters. A vapor filter of this type is a filter which is impermeable to fuel vapor. Furthermore, a tank ventilation system comprises an engine line Which leads from the vapor filter to an intake system or a suction system of the internal combustion engine and in which a controllable tank ventilation valve is arranged. So that such activated carbon filters do not lose their adsorption capability, they have to be purged or cleaned during operation of the engine.
It is known to act upon the activated carbon via the tank ventilation valve with negative pressure from a suction pipe of the suction system of the particular internal combustion engine, such that the activated carbon filter is purged via a fresh air line arranged in the remaining internal combustion engine system. Said purging air which is enriched with fuel vapor is supplied again in the region of the suction pipe of the internal combustion engine to the combustion. The activated carbon filter is therefore purged with ambient air via the negative pressurization of the suction pipe and, as a result, is passively regenerated. In this case, fuel vapors are supplied to the combustion depending on the negative pressure in the suction pipe. A disadvantage in this case is that, when there is low negative pressure in the suction pipe of the internal combustion engine, when the throttle valve is wide open, purging air sucked up via the activated carbon filter is insufficient to regenerate and purge the latter. Such a situation occurs, for example, in the case of supercharged engines, i.e. internal combustion engines in the supercharged mode, since there is then scarcely any negative pressure in the corresponding suction system.